The invention relates to moisture detecting apparatus in general, and more particularly to improvements in apparatus which can be used to detect minute quantities of moisture, such as in the ppm (parts per million) range. Still more particularly, the invention relates to improvements in apparatus which can be utilized with advantage for the determination of minute quantities of water in a coolant or refrigerant (hereinafter called coolant) which is circulated in the conditioning system of a motor vehicle, in the coolant conveying system of a refrigerator or in the coolant conveying system of another cooling machine.
It is well known that a circuit for a supply of coolant (e.g., Freon) which contains fluorohydrocarbons should not contain any moisture. At most, its water content can be in the parts per million range, namely well below a so-called critical water content range. If the coolant contains an excessive percentage of moisture, the moisture can exert an adverse influence upon the coolant and can lead to damage to, or even complete destruction of, the conditioning or refrigerating system. Therefore, it is necessary and customary to monitor the percentage of moisture in the circulating coolant. In accordance with heretofore known proposals, the monitoring is carried out optically by resorting to so-called indicator substances or materials which are contacted by coolant and the optical properties of which change as a result of contact with moisture in the coolant. Presently known indicator substances include cobalt bromide or cobaltous bromide (CoBr.sub.2) and cobalt chloride or cobaltous chloride (CoCl.sub.2). These indicator substances can be used with advantage to indicate the presence of minute quantities of water in Frigen 12 (Trademark) or in other types of coolants which contain fluorohydrocarbons. When the coolant which contacts an indicator substance consisting of or containing cobalt bromide or cobalt chloride carries minute quantities of moisture, the indicator substance undergoes a color change which is attributable to stepwise shifting of hydration water to thus induce a stepwise change of color of the metallic salt. Presently known proposals to ascertain the presence of minute quantities of moisture in coolant include the utilization of color indicators in the form of tablets containing cobalt bromide in or on a suitable substrate and being installed in the flow of coolant in such a way that the color of the tablet can be observed by a person looking through a window or the like. The relationship between the accumulation of hydration water and the changes of color is as follows:
CoBr.sub.2 =green; PA1 CoBr.sub.2 .times.1H.sub.2 O=blue; PA1 CoBr.sub.2 .times.2H.sub.2 O=purple; PA1 CoBr.sub.2 .times.6H.sub.2 O=pink.
Moisture detecting apparatus of the above outlined character are suitable for use in large or huge conditioning or refrigerating systems but are not suitable at all for installation in conditioning systems of motor vehicles and/or in cooling systems of refrigerators or other cooling machines. For example, the presence of water in a coolant-containing and conveying circuit can be attributable to a leak in the circuit, to diffusion, to dissociation or segregation and/or to splitting off and/or hydrolysis; this necessitates undertakings which can involve, for example, preventing the escape of coolant into the atmosphere or removing the moisture.
Published UK patent application No. GB 2 129 128 A of Hedges discloses a moisture detector which contains cobalt chloride and employs a radiation source in the form of a light emitting diode. Light which is emitted by the diode is reflected by cobalt chloride and is directed against a detector in the form of a photo transistor. A blue pass optical filter can be installed between the light emitting diode and the supply of cobalt chloride.
Swiss Pat. No. 666 752 to Groninger discloses a relative humidity detector which employs a light source, a carrier of moisture-sensitive salts and a photoelectric element which serves to correlate the emission and absorption spectra in such a way that the maxima or absolute maxima in the spectral region of the carrier are located in the range of 400 to 900 nm and are spaced apart by not more than 200 nm. The light source, the carrier and the photoelectric element are installed in a housing containing a foil which is permeable to water vapors and contains dissolved moisture-sensitive salts. The foil is sealed in the housing and is exposed to light which issues from the light source. Slots in the housing enable atmospheric air to contact portions of the foil so that water molecules in the air can reach the salts in the foil by capillary action to initiate a color change. The patented apparatus is not intended for use, and cannot be installed, in conditioning or refrigeration systems.